Open AccessVol 10 No 3 Research Identification and characterisation of the high-risk surgical population in the United Kingdom Rupert M Pearse1, David A Harrison2, Philip James3, David
Trang 1Open Access
Vol 10 No 3
Research
Identification and characterisation of the high-risk surgical
population in the United Kingdom
Rupert M Pearse1, David A Harrison2, Philip James3, David Watson1, Charles Hinds1,
Andrew Rhodes4, R Michael Grounds4 and E David Bennett4
1 William Harvey Research Institute, Queen Mary's School of Medicine and Dentistry, London, UK
2 Intensive Care National Audit & Research Centre, London, UK
3 CHKS Ltd, Alcester, Warwickshire, UK
4 Intensive Care Unit, St George's Hospital, London, UK
Corresponding author: Rupert M Pearse, rupert.pearse@bartsandthelondon.nhs.uk
Received: 23 Mar 2006 Accepted: 25 Apr 2006 Published: 2 June 2006
Critical Care 2006, 10:R81 (doi:10.1186/cc4928)
This article is online at: http://ccforum.com/content/10/3/R81
© 2006 Pearse et al.; licensee BioMed Central Ltd
This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Introduction Little is known about mortality rates following
general surgical procedures in the United Kingdom Deaths are
most common in the 'high-risk' surgical population consisting
mainly of older patients, with coexisting medical disease, who
undergo major surgery Only limited data are presently available
to describe this population The aim of the present study was to
estimate the size of the high-risk general surgical population and
to describe the outcome and intensive care unit (ICU) resource
use
Methods Data on inpatient general surgical procedures and
ICU admissions in 94 National Health Service hospitals
between January 1999 and October 2004 were extracted from
the Intensive Care National Audit & Research Centre database
and the CHKS database High-risk surgical procedures were
defined prospectively as those for which the mortality rate was
5% or greater
Results There were 4,117,727 surgical procedures; 2,893,432
were elective (12,704 deaths; 0.44%) and 1,224,295 were
emergencies (65,674 deaths; 5.4%) A high-risk population of
513,924 patients was identified (63,340 deaths; 12.3%), which
accounted for 83.8% of deaths but for only 12.5% of procedures This population had a prolonged hospital stay (median, 16 days; interquartile range, 9–29 days) There were 59,424 ICU admissions (11,398 deaths; 19%) Among admissions directly to the ICU following surgery, there were 31,633 elective admissions with 3,199 deaths (10.1%) and 24,764 emergency admissions with 7,084 deaths (28.6%) The ICU stays were short (median, 1.6 days; interquartile range, 0.8–3.7 days) but hospital admissions for those admitted to the ICU were prolonged (median, 16 days; interquartile range, 10–
30 days) Among the ICU population, 40.8% of deaths occurred after the initial discharge from the ICU The highest mortality rate (39%) occurred in the population admitted to the ICU following initial postoperative care on a standard ward
Conclusion A large high-risk surgical population accounts for
12.5% of surgical procedures but for more than 80% of deaths Despite high mortality rates, fewer than 15% of these patients are admitted to the ICU
Introduction
Reducing mortality following major surgery remains a
signifi-cant challenge for the National Health Service (NHS) The
number of deaths identified each year by the National
Confi-dential Enquiry into Peri-Operative Deaths (NCEPOD)
changed little between 1989 and 2003 [1,2] A recent
analy-sis identified higher mortality rates in a UK hospital when
com-pared with a similar institution in the USA [3] Approximately 2.3 million surgical procedures are performed annually in the NHS, with an estimated mortality of 1.4% [4] It is probable, however, that this low overall mortality rate conceals the exist-ence of a subpopulation at much greater risk of postoperative complications and death Successive NCEPOD reports show that the majority of deaths occur in older patients who undergo HRG = Healthcare Resource Group; ICNARC = Intensive Care National Audit & Research Centre; ICU = intensive care unit; NCEPOD = National Confidential Enquiry into Peri-Operative Deaths; NHS = National Health Service.
Trang 2major surgery and who have severe coexisting disease [1,2].
The few available estimates suggest mortality rates of between
5.8% and 25% for this high-risk surgical population [5-11]
While the publication of surgeon-specific mortality data for
cardiac surgery is a matter of public debate [12], other
surgi-cal specialties do not routinely collect such data The
NCE-POD provides information on those patients who die, but
provides no indication of the size of the high-risk surgical
pop-ulation from which they are derived Recent developments in
perioperative care may significantly improve outcome for these
patients [13,14]; however, in the absence of data describing
the size of the high-risk population, it is difficult to convince
cli-nicians and managers either of the need to introduce new
ther-apeutic approaches or to provide additional resources for
postoperative care The aim of the present study was to
ascer-tain what proportion of general surgical patients are at high
risk of postoperative death
Materials and methods
Data were extracted from two large healthcare databases, one
maintained by CHKS Ltd and the other maintained by the
Intensive Care National Audit & Research Centre (ICNARC)
CHKS provides comparative benchmarking services to NHS
trusts Data are created by a clerical coding method, similar to
Hospital Episodes Statistics Validation is performed locally by
the Trust and centrally by CHKS Ltd to provide a
quality-assured dataset that can be used to inform managerial and
clinical decisions The ICNARC case mix programme collects
data on consecutive admissions to participating adult, general
intensive care units (ICUs) in England, Wales and Northern
Ireland Data are collated locally by trained dedicated staff and
are subject to local and central internal error checks [15]
Data were extracted on all adult surgical admissions to hospi-tal (CHKS data) and to the ICU (ICNARC data) for 94 NHS hospitals in England, Wales and Northern Ireland between January 1999 and October 2004 inclusive These hospitals were selected because they contributed to both databases throughout the study period Admissions involving endoscopy, day-case surgery, cardiothoracic surgery, neurosurgery, organ transplantation, obstetrics or the surgical management of burns were excluded For brevity, procedures that satisfied the inclusion criteria are described as general surgical procedures
There are 6,920 surgical procedure codes in the Office of Population Censuses and Surveys (now part of Office for National Statistics and Surveys) classification Surgical admis-sions to hospital were identified in the CHKS database by the presence of one of 4,910 codes that satisfied the inclusion cri-teria Where more than one surgical procedure was performed during the same hospital admission, only the first procedure was included in the analysis Several alternative Office of Pop-ulation Censuses and Surveys codes may exist for any given procedure In order to reduce bias arising from discrepancies
in the coding process, procedures were categorised into one
of 372 Healthcare Resource Groups (HRGs) based on clini-cal similarity and resource homogeneity Many Office of Popu-lation Censuses and Surveys codes and HRG codes specify the presence of a complicating medical condition, the com-plexity of surgery or a particular age group HRGs were then ranked according to mortality rates High-risk surgical proce-dures were prospectively defined as those proceproce-dures included in an HRG with a mortality rate of 5% or more The remaining procedures were classified as standard risk
Figure 1
Mortality rates for general surgical patients identified from the CHKS
and ICNARC databases
Mortality rates for general surgical patients identified from the
CHKS and ICNARC databases CHKS database: standard, all
patients admitted to hospital for a general surgical procedure with an
overall mortality rate of less than 5%; high risk, subpopulation of
patients undergoing a procedure with an overall mortality rate of 5% or
more ICNARC database: ICU, general surgical patients admitted
directly to the intensive care unit following surgery; ward to ICU,
patients admitted to the intensive care unit following initial
postopera-tive care on a standard ward.
Figure 2
Duration of hospital stay for general surgical patients identified from the CHKS and ICNARC databases
Duration of hospital stay for general surgical patients identified from the CHKS and ICNARC databases CHKS database: standard,
all patients admitted to hospital for a general surgical procedure with an overall mortality rate of less than 5%; high risk, subpopulation of patients undergoing a procedure with an overall mortality rate of 5% or more ICNARC database: ICU, general surgical patients admitted directly to the intensive care unit following surgery; ward to ICU, patients admitted to the intensive care unit following initial postopera-tive care on a standard ward.
Trang 3Surgical admissions to the ICU were identified in the ICNARC
database by the source of admission (either operating theatre
or operating theatre via ward), and were only included if the
primary reason for admission was not an excluded surgical
procedure ICU admissions were prospectively divided into
admissions directly to the ICU following surgery and
admis-sions to the ICU following a period of postoperative care on a
standard ward Where patients were readmitted to the ICU,
only the first admission was included in the analysis
Data are presented as the median (interquartile range)
Cate-gorical data were tested with the chi-squared approximation,
and continuous data were tested with the Mann–Whitney U
test Analysis was performed using GraphPad Prism version 4.0 (GraphPad Software, San Diego, CA, USA) Significance
was set at P < 0.05.
Results
CHKS dataset
During the 70 months of the study, there were 4,117,727 hos-pital admissions involving a general surgical procedure, with 78,378 deaths (1.9%) The median age was 56 (39–71) years, and 1,784,909 patients were male (43%) There were 2,893,432 elective surgical admissions, with 12,704 deaths
Table 1
Data for two populations of general surgical patients identified from the CHKS database
Data presented as median (interquartile range) or n (%) Standard population, all patients admitted to hospital undergoing a procedure with an
overall mortality rate of less than 5%; high-risk population, patients undergoing a procedure with an overall mortality rate of 5% or greater.
Table 2
Mortality rates for selected Healthcare Resource Group procedure codes
F33: Large intestine; major procedures with complicating condition(s) 5,765 Emergency 1,290 22.38
F41: General abdominal; very major or major procedures aged over 69
years or with complicating condition(s)
H33: Neck of femur fracture; aged over 69 years or with complicating
condition(s)
L02: Kidney major open procedure; aged over 49 years or with
complicating condition
L27: Prostate transurethral resection; aged over 69 years or with
complicating condition
B02: Phakoemulsification cataract extraction with lens implant 89,444 Elective 50 0.06
F82: Appendicectomy procedures; aged less than 70 years with no
complicating condition
Data extracted from CHKS database Note that several Hospital Resource Group codes may exist for any given procedure; as a result, these data may not accurately describe mortality rates for a specific procedure.
Trang 4(0.44%), and 1,224,295 emergency admissions, with 65,674
deaths (5.4%) (Figure 1) The duration of the hospital stay was
greater for emergency admissions than for elective admissions
(5 (2–15) days versus 3 (1–6) days, P < 0.0001) The
dura-tion of hospital stay data for both datasets are presented in
Figure 2
Eighty-one out of 372 HRGs were associated with a mortality
rate of 5% or greater From these, 513,924 high-risk surgical
procedures were identified, accounting for 83.8% of deaths
but for only 12.5% of admissions (Table 1) Mortality rates
were much greater in the high-risk population than in the
standard population Patients in the high-risk population were
older, more likely to undergo emergency surgery and remained
in hospital for prolonged periods Complex or major surgery,
advanced age, the presence of a complicating medical
condi-tion or a combinacondi-tion of these factors was specified by 51 of
the 81 (63%) high-risk HRGs, compared with 95 of 291
(33%) standard-risk HRG codes Mortality rates for a
representative selection of HRG procedure codes are
pre-sented in Table 2
ICNARC dataset
Of 67,555 surgical admissions to the ICU, there were 59,424
general surgical admissions with 11,398 deaths (19%) Of
these deaths, 4,653 (40.8%) occurred after initial discharge
from the ICU; 3,529 patients were subsequently readmitted to
the ICU, with 1,332 deaths (37.7%) The median age was
68.7 (56.3–76.8) years, and 35,156 patients were male
(59.2%) There were 56,397 admissions directly to the ICU:
31,633 following elective surgery, with 3,199 deaths (10.1%),
and 24,764 following emergency surgery, with 7,084 deaths
(28.6%) (Figure 1) A further 3,027 patients were admitted to
the ICU following initial postoperative care on a standard
ward Of these, 1,766 followed elective surgery, with 643
deaths (36.4%), and 1,261 followed emergency surgery, with
472 deaths (37.4%) (Figure 1)
For elective ICU admissions, the duration of the ICU stay was
1.1 (0.8–2.4) days and the duration of hospital stay was 15
(10–26) days For emergency ICU admissions the duration of
the ICU stay was 2.1 (0.9–5.6) days and the duration of the
hospital stay was 18 (10–35) days (Figure 2) There were
3,283 early discharges from the ICU because of bed
short-ages (6.2%) but only 338 (0.7%) discharges from the ICU for
palliative care There were 7,807 discharges to
high-depend-ency units that did not contribute data to the ICNARC
data-base (14.8%)
Discussion
This study confirms the existence of a large population of
high-risk surgical patients with a hospital mortality rate of 12.3%
This population accounts for 83.8% of deaths but for only
12.5% of hospital admissions Assuming the hospitals used in
this analysis are representative of all the hospitals in the United
Kingdom where general surgical procedures are performed, it
is estimated that there are 1.3 million general surgical proce-dures per annum, with 25,000 deaths Of these, 166,000 would be high-risk surgical procedures according to the defi-nition used in this analysis High mortality rates relate to advanced age, comorbidities and the complex nature of the surgery, which is often performed as an emergency
Although these risk factors are well described [1,2], only a small proportion of this high-risk population was admitted to the ICU Mortality rates among general surgical admissions to the ICU were higher still, and yet the duration of the ICU stay was short It seems that patients were often discharged to the ward prematurely Prolonged hospital stays occurred in both the overall high-risk population and in patients admitted to the ICU This suggests that such patients have prolonged and complex medical needs Among ICU patients more than 40%
of deaths occur after initial discharge from the ICU, while less than 1% of ICU patients are discharged for palliative care The observation that only 6.2% of patients were classified as hav-ing been discharged from the ICU prematurely suggests we are not able to identify those patients who require continued ICU care The highest mortality rates were identified in the group of patients admitted to the ICU following initial care on
a standard ward following surgery The findings of this study are consistent with current mortality estimates for this popula-tion [1-11,16], and confirm the suggespopula-tion that the high-risk surgical population is much larger than previously thought Poor outcomes among the high-risk general surgical popula-tion are emphasised by comparison with cardiac surgery Although cardiac surgical patients undergo major surgery and have a high incidence of coexisting disease, this population has an overall mortality rate of only 3.5% (excluding surgery for congenital heart disease) and a mortality rate of just 2.0% for patients undergoing coronary artery bypass grafting [17] Sev-eral factors may account for this difference, but the availability
of dedicated ICU facilities is likely to be of particular impor-tance While ICU admission following cardiac surgery is rou-tine, provision of critical care facilities for major general surgery is limited These findings emphasise the importance of recognising patients who are at high risk of postoperative complications and death, and ensuring they receive an appro-priate level of postoperative care This issue has also been highlighted by NCEPOD reports, which identify inadequate provision of ICU resources as a factor in postoperative death [1,2]
While the benefit of postoperative critical care admission may seem self-evident to some, others suggest this remains to be proven Indeed, there is little evidence that the wider availabil-ity of critical care facilities improves the life expectancy of any large population A recent study from North America, however, has explored the determinants of long-term survival following major surgery [18] In a population of 105,000 surgical
Trang 5patients, the occurrence of complications within 30 days of
major surgery was found to be a much more important
deter-minant of long-term survival than either preoperative
comorbid-ity or intraoperative adverse events The authors of this report
conclude that healthcare resources should therefore be
focused on the prevention of complications Recent
develop-ments in postoperative critical care suggest that a
considera-ble reduction in postoperative complication rates may be
possible [13,14]
There are limitations with the use of data extracted from large
healthcare databases In the absence of a more reliable
sys-tem for estimating postoperative mortality rates, however, it is
necessary to rely on data currently available Difficulties with
the use of Hospital Episodes Statistics and similar data in the
identification of postoperative deaths are well recognised In
particular, the coding process is not designed to capture
detailed mortality data, although this appears to result in an
underestimate of mortality rates [1,2,17,19]
Data provided by CHKS are subject to similar limitations, but
may be more accurate than those extracted from the Hospital
Episodes Statistics database NHS Trusts work together with
CHKS to validate data, which are collated for the purpose of
assessing Trust performance rather than to satisfy statutory
requirements Data extracted from the ICNARC database
pro-vide an accurate description of ICU admissions and resource
use, although 14.8% of patients were discharged from the
ICU to high-dependency units that did not contribute data to
ICNARC This observation suggests that ICNARC data may
underestimate provision of critical care resources for surgical
patients This factor can, however, only account for a small
proportion of the short fall in critical care resource provision for
high-risk surgical patients While there are fewer
high-depend-ency unit beds than ICU beds in the United Kingdom [16],
data from this study suggest that the number of high-risk
pro-cedures may be more than eight times the number of ICU
admissions It is possible that not all admissions identified in
each database were drawn from the same population
Conse-quently, only a limited and cautious interpretation of the
com-bined dataset has been performed
Conclusion
The present study confirms the existence of a large population
of high-risk general surgical patients, which accounts for
around 13% of surgical admissions but more than 80% of
postoperative deaths Only a small proportion of this
popula-tion is admitted to the ICU, suggesting inadequate critical care
resource provision Better preoperative identification of these
high-risk patients is required Furthermore, an accurate system
is needed to collect mortality data for all surgical specialties
Competing interests
The authors declare that they have no competing interests
Authors' contributions
All authors were involved in data analysis and drafting the man-uscript, and approved the final version All authors had full access to data and take responsibility for the integrity of the data and the accuracy of the analysis
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Eng-Key messages
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• Over 80% of postoperative deaths occur in a subpopu-lation of high-risk surgical patients
• Fewer than 15% of these high-risk patients are admit-ted to intensive care following surgery
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